Technical Field
The present invention relates to a high voltage wire and relates particularly to a small diameter high voltage insulated electric wire excellent in flexibility and wear resistance.
Related Art
A high voltage wire as a component of a wire harness used in a high voltage portion of a hybrid vehicle, an electric vehicle, and so on is required to have heat aging resistance (heat-resistant life), flexibility, wear resistance, and so on. Along with downsizing of equipment and apparatuses, the high voltage wire is required to be lightened and further required to have a small diameter so as to be arranged in a narrow space. In order to reduce environmental load, the high voltage wire is furthermore required to be made of a halogen-free material containing no halogenated substance.
As a conventionally used high voltage wire, there has been proposed a cross-linked thin-walled wire which has an insulating layer formed of a flame retardant, which may be a non-halogenated flame retardant such as magnesium hydroxide, in ethylene copolymer resin such as ethylene-ethyl acrylate copolymer resin (EEA) and ethylene-vinyl acetate copolymer resin (EVA) (refer to JP 2525982 B2). However, the heat-resistant temperature of the cross-linked thin-walled wire is insufficient when this wire is used in a high voltage portion for a hybrid vehicle and an electric vehicle. Further, it is predicted that the composition of the cross-linked thin-walled wire does not satisfy required wear resistance.
As a conventionally used high voltage wire, there has been proposed a cross-linked heat-resistant wire which has an insulating layer, consisting of a bromine-based flame retardant and an antioxidant, in thermoplastic polyester (refer to JP 3439352 B2). However, since the cross-linked heat-resistant wire uses the bromine-based flame retardant, a high voltage wire is not made of a halogen-free material. The cross-linked heat-resistant wire has poor flexibility due to its high elasticity, and this electric wire is hardly wired and difficult to handle.
As a conventionally used high voltage wire, a cross-linked heat-resistant wire which has an insulating layer of fluororesin has been proposed (refer to JP 2909576 B2). However, since the cross-linked heat-resistant wire uses fluororesin, although the electric wire has sufficient heat resistance, the cost is high, and the flexibility is poor.
A heat aging resistance problem is that polyethylene (PE) and polypropylene (PP) cannot satisfy the heat aging resistance at 150° C. for 3000 hours. In order to address the heat aging resistance problem, a highly heat-resistant resin such as engineering plastic-type resins and super engineering plastic-type resins is required to be used. However, the highly heat-resistant resin is hard to significantly reduce flexibility and, in addition, is expensive; therefore, it is difficult to use the highly heat-resistant resin alone in an electric wire insulator.
A flexibility problem is that flexibility and wear resistance are in tradeoff relationship with each other, and in order to improve the wear resistance, a high voltage wire is often formed of a high elastic modulus material as a hard resin component; therefore, the flexibility cannot be secured. If the high voltage wire is used in an environment where high voltage is applied, the high voltage wire having a larger size is used, so that the hardness of the high voltage wire is further increased, and workability cannot be secured.
As a wear resistance problem, the wear resistance is improved by reducing an amount of filler. However, in order to secure flame retardance, a halogenated flame retardant is required to be used. The use of the halogenated flame retardant increases environmental load, as described above, and thus it is not preferable. In addition, since the halogenated flame retardant is expensive, it is unsuitable for use in a high voltage wire. Since the wear resistance is reduced by thinning an electric wire structure, it is difficult to maintain wear resistance in a high voltage wire having a narrowed diameter.
A halogen-free problem is that the use of a bromine-based flame retardant provides an effect of obtaining a high level of flame retardance and improving wear resistance. However, the bromine-based flame retardant contains a halogen substance to increase environmental load, and therefore, it is not preferable to use the bromine-based flame retardant.